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  Perception is in the ear of the beholder
Less physically fit people tend to perceive approaching sounds as being closer than they really are, new research has found.

While the error in perceptual judgment causes some to underestimate the arrival time of whatever, or whoever, is making the sound, it may provide a potentially life-saving advantage.

"From an evolutionary perspective, this anticipatory error would have little cost and actually give the organism slightly more time than expected to prepare to engage or evade the source," says Associate Professor John Neuhoff of The College of Wooster.

Neuhoff will present the findings next month at the Acoustical Society of America meeting in Portland, Oregan.
Margin of safety

For the study, he and colleagues Katherine Long and Rebecca Worthington measured the physical fitness of test subjects using recovering heart rate after exercise and grip strength.

Participants listened to a "looming" tone moving toward them, and were asked to press a button when they thought the sound had moved directly in front of them.

Although 98% of all listeners pressed the button too soon, individuals with greater upper body strength and/or stronger cardiovascular systems waited longer, while subjects in worse physical shape gave themselves a greater "margin of safety".

This and other studies show women tend to push the button before men, and both sexes perceive receding, and therefore less threatening, sounds equally.

Neuhoff says the response to looming sounds is probably influenced by many factors, including spatial hearing skills, physical fitness, risk-taking tendencies and even practice-honed expertise. For example, he speculates traffic cops might perform better on the test than average listeners.

"The new finding here is that physical fitness does play a role," he says.

The behavioral mechanism probably isn't fixed, however, so if a person changes to a better diet and becomes more physically fit, Neuhoff predicts he or she would become better at predicting the arrival time of approaching sounds and sound-makers.

Conversely, as people grow older, he suspects they would press the button sooner, giving themselves more time to react.

People hear most other sounds in unique ways too. For example, "highly trained composers and musicians hear things in the music that novices do not," says Neuhoff.
Differently tuned

In a separate study, Jackson Gandour, a professor of linguistics at Purdue, applied functional brain imaging techniques to display cerebral blood flow as people heard and spoke their native language.

The scientists discovered that the melody of speech, especially noticeable in tonal languages such as Mandarin, engages multiple brain areas involving large-scale networks affecting the entire brain.

"Everyone has a brainstem, but it's tuned differently depending on what sounds are behaviorally relevant to a person, for example, the sounds of his or her mother tongue," says Gandour.

Neuhoff suspects that, among non-human animals, whether or not a creature holds prey or predator status could affect how it perceives approaching sounds. Wolves would probably ace the test, while bunnies would react like scrawny humans.

"The bunnies would need a larger margin of safety," he says.
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